1. Technical Field of the Invention
The present invention relates to a color liquid crystal panel suitably used as a display of a portable telephone, a method for manufacturing the same, and further a color liquid crystal display device employing the same, more particularly, to a color liquid crystal panel having an enhanced capability of displaying high quality images, a method for manufacturing the same, and further a color liquid crystal display device employing the same.
2. Description of the Related Art
It is conventionally known that a semi-transmissive liquid crystal display device consisting of a plurality of pixels, each having a transmissive display section and a reflective display section therein, has been developed as a liquid crystal display device equipped with both features of a transmissive liquid crystal display device and a reflective liquid crystal display device. In such a semi-transmissive liquid crystal display device, a color filter for a transmissive display section and a color filter for a reflective display section are provided corresponding to each color to be displayed and therefore, totally six kinds of color filters are to be provided corresponding to each color. Accordingly, in order to manufacture a color liquid crystal display device having the above-described construction of color filter, it is necessary that six kinds of photoresist films are prepared corresponding to those color filters and then, six photolithography steps are carried out. Consequently, there has been found a drawback in that the semi-transmissive liquid crystal display device manufactured in accordance with the above-described method results in a low yield and high manufacturing cost thereof.
In consideration of the above-stated drawback, the following semi-transmissive liquid crystal display device has recently been disclosed in publications such as Japanese Patent Application Laid-open No. 2000-111902. That is, a semi-transmissive liquid crystal display device is constructed such that only one kind of color filter is formed corresponding to each color and a region in which no color filter exists is formed within a reflective display section.
FIG. 1 is a plan view illustrating a layout of a TFT substrate included in a conventional semi-transmissive liquid crystal display device disclosed in Japanese Patent Application Laid-open No. 2000-111902 and FIG. 2 is a cross sectional view of a liquid crystal panel employed in the conventional semi-transmissive liquid crystal display device, taken along the line A—A of FIG. 1.
In the conventional semi-transmissive liquid crystal display device disclosed in the publication, a red color pixel 101R, a green color pixel 101G and a blue color pixel 101B are disposed in this order in a direction in which a scanning signal line extends. In each pixel, a thin film transistor (TFT) 102 is formed. The thin film transistor 102 consists of a gate electrode 103a projecting from a gate line 103 as the scanning signal line and a drain electrode 104a projecting from a drain line 104 that extends in a direction perpendicular to the gate line. The gate line 103 and the gate electrode 103a are formed on a transparent substrate 100a and further, an insulation film 105 is formed on the transparent substrate 100a covering the gate line 103 and the gate electrode 103a. The drain line 104 is formed on the insulation film 105. An amorphous silicon layer 106 is formed on the insulation film 105 to face the gate electrode 103a and the drain electrode 104a is formed extending on the amorphous silicon layer 106. Furthermore, a source electrode 107 is formed extending from the amorphous silicon layer 106 in a direction apart from the drain electrode 104a while a part of the source electrode is at least positioned on and inside the amorphous silicon layer.
Within a reflective display section of each pixel, projecting portions 108 are formed on the insulation film 105 and within a transmissive display section, a transparent electrode 109 is formed on the insulation film 105. Note that the reflective display section is formed to surround the transmissive display section. Furthermore, within a region excluding the transmissive display section in each pixel, an insulation film 110 covering the projecting portions 108, the thin film transistor 102 and the like is formed and further, a contact hole 111 is formed in the insulation film 110 so as to reach the surface of the source electrode 107. A reflective electrode 112 is formed within the contact hole 111 and on the insulation film 105. The reflective electrode 112 has a convex-concave surface reflecting the profile of the projecting portions 108. The reflective electrode 112 is connected also to the transparent electrode 109. Furthermore, a retardation film 113 and a polarizer 114 are formed on the transparent substrate 100a on a side thereof defined as the surface on which elements such as the thin film transistor 102 are not formed. The elements constructed as described above constitute a TFT substrate.
Additionally, another transparent substrate 100b is disposed in parallel with the transparent substrate 100a on a side thereof defined as the surface on which the thin film transistor 102 is formed. A color filter (CF) 121 and an opposing electrode 122 are formed on a surface of the transparent substrate 100b on a side thereof facing the transparent substrate 100a. As shown in FIG. 1, the color filter 121 is formed extending in parallel with the drain line 104 and further, when viewing a pixel in a direction perpendicular to a surface of the associated transparent substrate, the transparent electrode 109 is being formed inside with respect to both end lines of the color filter 121 whereas the reflective electrode 112 is being formed to have a width extending beyond the both lines thereof. Furthermore, a retardation film 123 and a polarizer 124 are formed on the transparent substrate 100b on a side thereof defined as the surface on which elements such as the color filter 121 are not formed. The elements constructed as described above constitute a CF substrate.
In addition to the above-described construction of liquid crystal panel, a liquid crystal 130 is interposed between the TFT substrate and the CF substrate to constitute the liquid crystal panel.
The conventional color liquid crystal display device constructed as described above has one kind of color filter therein corresponding to each color and therefore, can be manufactured through a reduced number of process steps, thereby improving a yield thereof.
Furthermore, as the color filter 121 of the CF substrate employed in the above-described color liquid crystal display device has a region therein, facing the reflective electrode 112, in which the color filter 121 is not formed, the color liquid crystal display device can offer a display brightness greater than that could be achieved in a color liquid crystal display device developed before the emergence of color liquid crystal display device employing such construction of the color filter 121.
Moreover, the conventional reflective liquid crystal display device has projecting portions formed under the reflective electrode and extending in all directions. The projecting portions are designed to have a pattern optimal in terms of paths of an incident light and a reflected light. FIG. 3 illustrates a layout of projecting portions employed in the conventional liquid crystal display device. In a reflective liquid crystal display device, the projecting portions 108 are formed without especially taking into account the effect of boundaries between pixels. In addition, a liquid crystal display device having a transmissive display section and a reflective display section therein includes such projecting portions only within the reflective display section.
However, it has been found a problem in that the conventional semi-transmissive liquid crystal display device employing one kind of color filter corresponding to each pixel in order to, for example, reduce the number of process steps to be carried out to manufacture the device has an image quality inferior to that of a device employing two kinds of color filters therein, which has been developed before the emergence of the device employing one kind of color filter.
Furthermore, it has also been found another problem in that both a reflective liquid crystal display device and a semi-transmissive liquid crystal display device have displayed images appearing pale yellow in color thereon.